Flat-panel displays are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ an array of pixels distributed in rows and columns over a display substrate to display images, graphics, or text. In a color display, each pixel includes light emitters that emit light of different colors, such as red, green, and blue. For example, liquid crystal displays (LCDs) employ liquid crystals to block or transmit light from a backlight behind the liquid crystals and organic light-emitting diode (OLED) displays rely on passing current through a layer of organic material that glows in response to the current. Displays using inorganic light emitting diodes (LEDs) are also in widespread use for outdoor signage and have been demonstrated in a 55-inch television. Flat-panel electronic sensors having a plurality of pixel sensors are also available; for example, for digital radiography.
Flat-panel displays and other matrix-addressed systems such as imaging systems are typically controlled with either a passive-matrix (PM) control employing electronic circuitry external to the display substrate or an active-matrix (AM) control employing electronic circuitry formed directly on the display substrate and associated with each light-emitting element. Both OLED displays and LCDs using passive-matrix control and active-matrix control are available. An example of such an AM OLED display device is disclosed in U.S. Pat. No. 5,550,066.
Active-matrix systems are often found in large-format displays, such as liquid-crystal displays (LCDs) or organic light-emitting diode (OLED) displays. Such active-matrix displays typically comprise an array of pixel circuits (e.g., pixel controllers, micro-controllers) arranged in rows and columns on a display substrate in a display area. Each pixel circuit controls a light-controlling element. Each light-controlling element can be a single controllable light absorber, light reflector, or light emitter. A row-select line is electrically connected to each row of pixel circuits and a column-data line is electrically connected to each column of pixel circuits in the array of pixel circuits. Each row of pixel circuits is sequentially selected by the corresponding row-select line and data is provided to each pixel circuit in the row through the column-data line connected to the pixel circuit.
In these systems, each pixel circuit is electrically connected and responsive to a unique pair of a row-select and a column-data line that provides data corresponding to a desired luminance of the light-controlling elements in a selected row, stores the data in a pixel-control circuit, and controls a light-controlling element with the pixel circuit according to the stored data. In contrast, a passive-matrix system does not have a pixel circuit that stores data associated with each light-controlling element.
A paper entitled “AMOLED Displays with Transfer-Printed Integrated Circuits” (Cok et al, Journal of the Society for Information Display Digest, p. 335, 2011, 1071-0922/11/1904-0335, DOI #10.1889/JSID19.4.335), illustrates an OLED display with pixel controllers controlling a four-color pixel (red, green, blue, white) in response to analog signals provided on row-select and column-data lines. In this design, a single micro-transfer printed integrated circuit controls each four-color pixel and is responsive to two row-select and two column-data lines. In other designs, for example as illustrated in U.S. Pat. No. 8,599,118 and in U.S. Pat. No. 8,896,505, a single integrated circuit controls multiple multi-color LED pixels. An array of these integrated circuits and multi-color pixels form a light-emitting assembly such as a display comprising an array of light-emitting diode (LED) devices and an array of micro-controllers to switch and drive the array of LED devices, where the number of micro-controllers in the array of micro-controllers is less than the number of LED devices in the array of LED devices. Each micro-controller is electrically connected to a plurality of the multi-color pixels so that each micro-controller drives a plurality of multi-color pixels, each multi-color pixel comprising a plurality of LEDs, where each LED of the plurality of LEDs in a multi-color pixel emits light of a different color.
Active-matrix circuits are commonly constructed with thin-film transistors (TFTs) in a semiconductor layer formed over a display substrate and employing a separate TFT circuit to control each light-emitting pixel in the display. The semiconductor layer is typically amorphous silicon or poly-crystalline silicon and is distributed over the entire flat-panel display substrate. The semiconductor layer is photolithographically processed to form electronic control elements, such as transistors and capacitors. Additional layers, for example, insulating dielectric layers and conductive metal layers are provided, often by evaporation or sputtering, and photolithographically patterned to form electrical interconnections, or wires. For example, U.S. Pat. No. 8,421,791 discloses a matrix-addressed liquid crystal display and U.S. Pat. No. 6,448,718 discloses an active-matrix-addressed electro-luminescent display.
Typically, each display sub-pixel is controlled by one control element, and each control element includes at least one transistor. For example, in a simple active-matrix organic light-emitting diode (OLED) display, each control element includes two transistors (a select transistor and a power transistor) and one capacitor for storing a charge specifying the luminance of the sub-pixel. Each OLED element employs an independent control electrode connected to the power transistor and a common electrode. In contrast, an LCD typically uses a single transistor to control each pixel. Control of the light-emitting elements is usually provided through a data signal line, a select signal line, a power connection and a ground connection. Active-matrix elements are not necessarily limited to displays and can be distributed over a substrate and employed in other applications requiring spatially distributed control.
Inorganic light-emitting diode displays using inorganic micro-LEDs on a display substrate are also known. Micro-LEDs can have an area less than 1 mm square, less than 100 microns square, or less than 50 microns square or have an area small enough that it is not visible to an unaided observer of the display at a designed viewing distance. U.S. Pat. No. 8,722,458 entitled Optical Systems Fabricated by Printing-Based Assembly teaches transferring light-emitting, light-sensing, or light-collecting semiconductor elements from a wafer substrate to a destination substrate.
Active-matrix display control is typically provided by a display controller that in turn controls a column controller and a row controller. The column controller includes a column drive circuit for each column of pixels. Each column drive circuit is electrically connected to each pixel circuit in the column corresponding to the column drive circuit. Similarly, the row controller includes a circuit for selecting each row of pixels. Each row-selection circuit is electrically connected to each pixel circuit in the row corresponding to the row-selection circuit. In operation, the column controller supplies a data value to each column and the row controller energizes the row-selection circuit corresponding to the row of pixels for which the data values are intended. This arrangement, however, requires a separate electrical connection for each column and for each row. Thus, for an M×N pixel array, M+N electrical connections must be made to the array of pixels and generally to the substrate on which the flat-panel display is provided. For large displays, for example, having thousands of rows and columns of pixels, the cost of connecting the pixel rows and columns can be significant.
There is a need therefore for matrix-addressed system architectures that reduce the cost of controlling a display and the number and cost of electrical connections in a matrix-addressed system such as a flat-panel display or imaging system.